Clamshell type cartons generally have two sections, each section including a base panel, wall panels attached to the base panel, and connecting tabs formed at the corners of the wall panels; the two sections being separated by an articulated hinge. Such cartons are useful, for example, as containers for fast food items such as hamburgers and the like. The paperboard from which the carton is formed is normally printed with attractive graphics and coated (with a polyethylene coating or the like) to protect the product and to prevent absorption of liquid or food juices by the paperboard.
Cartons of the clamshell type present one particularly difficult forming problem not present when simple trays are being formed. That is, some means must be provided to fold and gather the articulated hinge of the carton blank in a rapid manner while not interfering with folding and gluing steps. The carton blank must be conveyed into proper contacting registration with the forming die and must be properly supported in the forming head path to accept the onset of the forming head.
While this approach has proven to be successful, one disadvantage of this prior art type apparatus is that it has an upper speed limitation due to the relatively complex folding and gluing operations which must be performed in the forming die to provide the completed hinged, clamshell type carton. For example, the carrier frame utilized to feed the paperboard blank onto the die must pivot through 90.degree. of movement into the forming head and must then pivot out of the die. Next, the hinge prebreaking blades must also pivot into and out of the die. The aforesaid feeding and blade movement must take place before the forming head begins its descending stroke. This built-in delay thus interferes with the high speed operation of the forming head, thereby increasing production time.